Sterling silver jewelry and utensils are valued because of their intrinsic worth and the silver color of the metal. The alloys from which sterling silver jewelry and utensils are made are preferably moldable and castable, yet hard enough for sterling silver jewelry. One problem with sterling silver is its tendency to tarnish. Another problem with sterling silver is the fact that sterling silver is usually brittle after casting. Sterling silver alloy is generally 92.5% silver and 7.5% copper, and many attempts have been made to improve the tarnish resistance and corrosion resistance of sterling silver and to improve the casting qualities of the alloy by the addition of other metals.
For example, alloys known as precium have been produced with approximately 74% silver, 25% PD and 1% IN. However, precium alloys have been found to be too expensive for substantial commercial use. A prior art, tarnish-resistant and corrosion-resistant silver-colored alloy is disclosed in U.S. Pat. No. 5,037,708, entitled “Silver Palladium Alloy.” The alloy in this prior art patent is made up of 80% to 92.5% silver, 4% to 9% palladium, 10% to 0% copper and 1% to 0.5% indium or zinc. U.S. Pat. No. 4,944,985 to Alexander discloses a silver alloy for plating that uses silica as an extender, but does not use pure metal silicate as in the present invention or for improved casting properties. Rather, silicate in combination with other materials is disclosed. Alexander et al. further discloses that ductility and smooth surface finish are desirable, but does not describe how to prevent brittleness. Further, Alexander et al. describes the use of silicates as extenders, which are defined as making casting easier and increasing the volume of the alloy using low-cost materials.
Japanese Patent No. 59038-346A teaches an alloy that has zinc and nickel. This prior art reference also uses indium and bismuth. While these prior alloys are useful, a sterling silver alloy that is less expensive would be an improvement over the prior.
Japanese Patent No. 62-243725 teaches a jewelry alloy with concentrations of silver, zinc, indium, and copper; however, its casting properties and melting are not well-suited for jewelry.